Method, device and system for establishing a bearer for a gsm network

ABSTRACT

A method for establishing a bearer for a GSM network is disclosed in embodiments of the present invention. The method includes: receiving, by a Media Gateway, a message for adding a wireless side end point, assigning an IP address and a port number for a call and transmitting a response message containing the IP address and the port number assigned for the call; acquiring, by the Media Gateway, the IP address and the port number assigned for the call by the Base Station Controller via the Mobile Switching Center Server and establishing an IP bearer with the Base Station Controller. A device and a system for establishing a bearer for a GSM network are also disclosed in embodiments of the present invention. With the present invention, a full or part path transcoder-free operation may be realized, which can avoid quality reduction and transmission delay.

CROSS REFERENCE TO RELATED APPLICATIONS

Priority is hereby claimed to the Chinese Patent Application No.200710006885.6 filed Feb. 2, 2007 and the Chinese Patent Application No.200710105889.X filed Jun. 1, 2007, which are incorporated by referenceherein in their entirety.

FIELD OF THE INVENTION

The present invention relates to GSM network interface technology,particularly to a method, a device and a system for establishing abearer for a GSM network.

BACKGROUND

In a conventional Global System for Mobile Communication (GSM) networksystem, the Base Station Controller (BSC) side is required to convertthe wireless side voice from compressed codes (such as HWFR/EFR codes)to non-compressed G.711 codes. The Media Gateway (MGW) on the corenetwork side is required to convert the non-compressed G.711 codes toAdaptive Multi-Rate (AMR) compressed codes. Furthermore, the MGW isrequired to convert the bearer mode between TDM bearer on one side andIP bearer on the other side. In order to realize these conversions, aTranscoder and Rate Adaption Unit (TRAU) or a TransCoder (TC) istypically inserted in the BSC of the GSM network system, and a TC isinserted in the MGW, for corresponding conversions of voice codes andbearer modes. Such conversions may lower voice quality, waste a lot ofcostly TC resources, and increase equipment costs. At the same time,since G.711 coding is used in the A interface, each path of the callsoccupies a bandwidth of 64 k, causing a waste of long-distancetransmission resources from the BSC to the MGW.

To save the TDM transmission resource between the BSC and the MGW, animproved method presently proposed is to move the TRAU from the BSC sideto the MGW side to collocate the TRAU with the MGW, and an Aterinterface is provided between the BSC and the TRAU for transmittingvoice and data in format of TRAU frames. Since each call of the Aterinterface occupies a bandwidth of only 16 k, four calls may bemultiplexed into one TDM slot, saving the valuable long-distancetransmission resource between the BSC and the MGW.

Although the improved method mentioned above solves the problem ofwasting the long-distance transmission resource between the BSC and theMGW, TCs are still required to be inserted in both the TRAU and the MGWfor the conversion of bearer modes, which also suffers voice qualitydeterioration and TC resource wasting due to multiple code conversions.

SUMMARY

An embodiment of the present invention provides a method forestablishing a bearer for a GSM network to improve voice quality.

Another embodiment of the present invention provides a base stationcontrol device to improve voice quality.

Another embodiment of the present invention further provides a MediaGateway device to improve voice quality.

Another embodiment of the present invention further provides a MobileSwitching Center server to improve voice quality.

Another embodiment of the present invention further provides a systemfor establishing a bearer for a GSM network to improve voice quality.

To achieve the above-mentioned objects, the technical solutionsaccording to embodiments of the present invention are specificallyimplemented as follows.

A method for establishing a bearer for a GSM network includes thefollowing steps:

receiving, by a Media Gateway, a message for adding a wireless side endpoint, assigning an IP address and a port number for a call, andtransmitting a response message containing the IP address and the portnumber assigned for the call; and

acquiring, by the Media Gateway, the IP address and the port numberassigned for the call by a wireless side Base Station Subsystem, andestablishing an IP bearer with the wireless side Base Station Subsystem.

A base station control device includes:

a receiving unit, configured to receive an assignment message andtransmit it to a processing unit;

a processing unit, configured to receive the assignment message, acquirethe IP address and the port number of the Media Gateway contained in themessage, assign the IP address and the port number for a call, initiatethe establishment of an IP bearer, and transmit an assignment responsemessage containing the IP address and the port number assigned for thecall by the equipment to a transmitting unit; and

a transmitting unit, configured to receive and transmit the assignmentresponse message.

A Media Gateway includes:

a receiving unit, configured to receive a message for adding a wirelessside end point and a bearer and code type modify message, and transmitthem to a processing unit;

a processing unit, configured to receive the message for adding awireless side end point, assign an IP address and a port number for acall, output a response message containing the IP address and the portnumber assigned for the call to a transmitting unit; receive the bearerand code type modify message, acquire information about the IP addressand the port number assigned for the call by the wireless side BaseStation Subsystem contained in the message, and establish IP bearer withthe wireless side Base Station Subsystem; and

a transmitting unit, configured to receive and transmit the responsemessage.

A Mobile Switching Center Server includes:

a receiving unit, configured to receive a call request containinginformation about the code types supported by a mobile station itselftransmitted by the mobile station, a response message containing the IPaddress and the port number assigned for the call returned by the MediaGateway and an assignment response message returned by the wireless sideBase Station Subsystem, and transmit them to the processing unit;

a processing unit, configured to establish a priority list of the codetype according to the call request message, transmit a message foradding a wireless side end point to the transmitting unit; generate anassignment message according to the received response message and thepriority list of the code type, and output the assignment message to thetransmitting unit; conduct code type negotiation according to thereceived assignment response message, and output information containingthe IP address and the port number assigned to the call by the wirelessside Base Station Subsystem to the transmitting unit; and

a transmitting unit, configured to receive and transmit to the MediaGateway the message for adding a wireless side end point and theinformation containing the IP address and the port number assigned forthe call by the Base Station Controller output by the processing unit;receive the assignment message output by the processing unit, andtransmit it to the wireless side Base Station Subsystem.

A system for establishing a bearer for a GSM network includes a BaseStation Controller, a Mobile Switching Center Server and a MediaGateway. The Mobile Switching Center Server is further configured toimplement IP-based interfaces between the Base Station Controller andthe Media Gateway, wherein:

the Mobile Switching Center Server is configured to receive a callrequest message containing information about code types supported by themobile station itself, transmit a message for adding a wireless side endpoint to the Media Gateway, receive the response message containing theIP address and the port number assigned for the call returned by theMedia Gateway, transmit the assignment message to the Base StationController; receive the assignment response message returned by the BaseStation Controller, conduct code type negotiation, and transmit theinformation containing the IP address and the port number assigned forthe call by the Base Station Controller to the Media Gateway;

the Media Gateway is configured to receive the message for adding awireless side end point transmitted by the Mobile Switching CenterServer, return the response message containing the IP address and theport number assigned for the call returned by the Mobile SwitchingCenter Server; receive information about the IP address and the portnumber assigned for the call by the Base Station Controller, andestablish IP bearer with the Base Station Controller; and

the Base Station Controller is configured to transparently transmit acall request message to the Mobile Switching Center Server, receive theassignment message transmitted by the Mobile Switching Center Server,acquire the IP address and the port number of the Media Gatewaycontained in the message, assign the IP address and the port number forthe call, initiate establishment of IP bearer, and transmit theassignment response message containing the IP address and the portnumber assigned for the call by the Base Station Controller to theMobile Switching Center Server.

As can be seen from the technical solutions mentioned above, with themethod, equipment and system for establishing GSM network bearer inembodiments of the present invention, by using IP bearer at the Ainterface between the BSC and the MGW to directly transmit HR/FW/EFRcompression voice codes at the A interface, wasting of TC resources iseffectively decreased, transcoder-free operation (TrFO) for full path orhalf path of the voice channel between BSCs on the calling and calledsides is realized, and the voice quality is enhanced and equipment costsare saved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the GSM network architecture in theapplication of a method embodiment of the present invention.

FIG. 2 is a diagram illustrating the improved GSM network structure onthe calling/called side in the application of a method embodiment of thepresent invention.

FIG. 3 is a diagram illustrating the system stricture of the GSM networkwith IP-based interfaces according to an embodiment of the presentinvention.

FIG. 4 is another diagram illustrating the architecture of the BSCaccording to an embodiment of the present invention.

FIG. 5 is another diagram illustrating the architecture of the BSCaccording to an embodiment of the present invention.

FIG. 6 is a diagram illustrating the architecture of the MGW accordingto an embodiment of the present invention.

FIG. 7 is another diagram illustrating the architecture of the MGWaccording to an embodiment of the present invention.

FIG. 8 is a diagram illustrating the architecture of the MSC serveraccording to an embodiment of the present invention.

FIG. 9 is a diagram illustrating the system structure of the GSM networkwith an IP-based A interface according to the first embodiment of thepresent invention.

FIG. 10 is a diagram illustrating the hierarchical structure of theprotocol stack of the signaling plane and the bearer plane of the Ainterface of the system shown in FIG. 9 according to an embodiment ofthe present invention.

FIG. 11 is a diagram illustrating the system structure of the GSMnetwork with an IP-based A interface according to the second embodimentof the present invention.

FIG. 12 is a diagram illustrating the voice message encapsulationstructure at the Abis interface according to the second embodiment ofthe present invention.

FIG. 13 is a diagram illustrating the 2 G to 2 G calling procedureaccording to the second embodiment of the present invention.

FIG. 14 is a diagram illustrating first architecture of the user planeprotocol stack of the Nb interface according to the second embodiment ofthe present invention.

FIG. 15 is a diagram illustrating a networking structure of interworking2 G and 3 G according to the second embodiment of the present invention.

FIG. 16 is a diagram illustrating second architecture of the user planeprotocol stack at the Nb interface according to the second embodiment ofthe present invention.

FIG. 17 is a diagram illustrating third architecture of the user planeprotocol stack at the Nb interface according to the second embodiment ofthe present invention.

FIG. 18 is a diagram illustrating the system structure of the GSMnetwork with an IP-based Ater interface according to the thirdembodiment of the present invention.

FIG. 19 is a diagram illustrating the system stricture of the IP-basedGSM network according to the fourth embodiment of the present invention.

FIG. 20 is a diagram illustrating the system structure of the IP-basedGSM network according to the fifth embodiment of the present invention.

FIG. 21 is a diagram illustrating the procedure of signaling processingwith the TC arranged at the BSC side according to an embodiment of thepresent invention.

FIG. 22 is a diagram illustrating the procedure of signaling processingwith the TC arranged at the MGW side according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

In order to make the objects, technical solutions and advantages of thepresent invention clearer, a detailed description of the presentinvention is provided below with reference to the figures andembodiments.

The GSM system defined by the Third Generation Partnership Project(3GPP) standardization organization mainly consists of three parts: aMobile Switching Subsystem (MSS), a Base Station Subsystem (BSS) and aMobile Station (MS). FIG. 1 is a diagram illustrating the GSM networkarchitecture in the application scenario of a method embodiment of thepresent invention. As shown in FIG. 1, the system includes an MSS, a BSSand an MS. The MSS implements the main switching functions of GSM, andat the same time manages subscriber data and a database required formobility. The MSS also manages communications between GSM mobilesubscribers and communications between a GSM mobile subscriber and asubscriber of another communication network. The MSS includes a MobileSwitching Center (MSC) server and an MGW. The BSS includes a BSC and aBase Transceiver Station (BTS). The BSC interfaces with the wirelessnetwork and is responsible for the management of the wireless networkand wireless resources. The BSC is also responsible for managing theestablishment, the connection and the releasing of calling/called MSsand BTS wireless connections on the calling/called side, providingfunctions such as voice coding, code type conversion and rateadaptation. The BTS performs conversion between the BSC and the wirelesschannel, and performs wireless transmission over the air interfacebetween the BTS and MSs and realizes related control functions.

The interface between the BTS and the BSC is an Abis interface thattransmits GSM voice and data messages with Time Division Multiplexing(TDM) codes and Channel Codec Unit (CCU) protocol frames. Each CCUchannel occupies a bandwidth of 16 k. Voice coding formats include HalfRate (HR), Full Rate (FR) and Enhanced Full Rate (EFR) coding. Theinterface between the BSS and the MSC server is an A interface. On theside of the MGW where the MGW is connected with the BSC, the A interfacebetween the BSC and the MGW is an MGW wireless side end point thattransmits voice and data with TDM G.711 protocol. The coding method isG.711 and each call occupies a bandwidth of 64 kbps.

On the MSS side, the MSC server and the MGW use a mode of 3GPP R4 inwhich the bearer and the control are separated. All signaling controlsare processed by the MSC server, and all bearers are processed by theMGW. An Nb interface is used between the MGW and another MGW. The codingmethod is typically AMR coding. An Internet Protocol (IP) transmissionmode is used to increase transmission efficiency and save bandwidth. AnNc interface is used between the MSC server and the MGW. An A interfaceis used between the MSC server and the BSC for the bearing of messagessuch as messages about user's connection requests and messages aboutdisconnection commands by transmitting the Base Station SubsystemApplication Part (BSSAP) signaling. After being processed by the BSC,the messages are sent to the BTS. The BSSAP messages are defined by theGSM08.08 specification. An Nc interface is used between the MSC serverand another MSC server to solve the problem of separate call controlsand bearer controls using the Bearer Independent Call Control (BICC)protocol. The bearing of call control signaling on various networks isproposed for applications of telephone services, which may provide goodtransparency for implementing services of existing circuit-switchedtelephone networks in NGN.

FIG. 2 is a diagram illustrating the improved GSM network structure onthe calling/called side in the application scenario of the methodembodiment of the present invention. As shown in FIG. 2, an Aterinterface is used between the BSC and the TRAU to transmit voice anddata in format of TRAU frames. The original interfaces and bearer modesbetween the TRAU and the MGW remain unchanged. Since each call at theAter interface occupies only a bandwidth of 16 k, four calls may bemultiplexed into one TDM slot, hence saving the valuable long-distancetransmission resources between the BSC and the MGW.

Embodiments of the present invention may effectively mitigate thewasting of TC resources and achieve full path or half path TrFO for thetelephone channel by realizing the IP-based A interface between the BSCand the MGW and directly transmitting wireless side compressed voicecodes such as HR/FR/EFR codes.

The present invention proposes a system for establishing a bearer for aGSM network. Changing interfaces of the GSM network into IP-basedinterfaces includes establishing an IP bearer and implementing code typenegotiation. Media services and signaling are transmitted through the IPbearer, and the problem of voice quality deterioration due to thetranscoding TC is solved.

FIG. 3 is a diagram illustrating the system stricture of the GSM networkwith IP-based interfaces according to an embodiment of the presentinvention. Referring to FIG. 3, the system includes an MS, a BTS, a BSC,an MSC server and an MGW.

The MS is configured to transmit a call request message carryinginformation about the code types it supports to the BSC and receive amessage returned by the MSC server indicating that the call is beingprocessed.

The BTS is configured to transparently transmit the call request messagesent by the MS and the message sent by the MSC server indicating thatthe call is being processed.

The BSC is configured to establish an IP bearer with the MGW andimplement code type conversion, receive the call request messagetransmitted by the MS, transparently transmit it to the MSC server,receive and forward the message transmitted by the MSC server indicatingthat the call is being processed; and receive an assignment messagetransmitted by the MSC server. If the interface between the BSC and theMGW is determined to be an A interface, the IP address and the portnumber of the wireless side of the MGW is obtained and the IP addressand the port number of its own are assigned for the call, and an IPbearer is established.

If the interface between the BSC and the MGW is determined to be an Aterinterface, the establishment of the Ater interface channel between theBSC and the MGW is negotiated using in-band signaling of the bearerplane through TRAU signaling (the in-band signaling between the BSC andthe MGW may be established in advance). The IP address and the portnumber assigned for the call by the MGW are acquired and the IP addressand the port number of its own are assigned for the call. The MGWacquires the IP address and the port number assigned for the call by theBSC via the Ater interface channel and an IP bearer is established.Alternatively, the Ater interface between the BSC and the MGW issimulated as an A interface, and the BSC receives the assignmentmessage, acquires the IP address and the port number of the wirelessside of the MGW and assigns the IP address and the port number of itsown of the Ater interface side for the call, and an IP bearer isestablished.

An assignment message transmitted by the MSC server is received. A codetype is selected according to priority list of the code type or its ownpolicy, and the code type selected by the BSC is fed back to the MSCserver through an assignment response message. If the selected code typeis consistent with the code type with the highest priority in thepriority list of the code type, the TrFO in this segment is realized andthe transparent transmission of media stream is accomplished; otherwise,a message for changing the code type is received from the MSC server andcode type conversion between the code type selected by the BSC and thecode type required by the MSC server is performed.

The MSC server separates the bearer and the control, and is configuredto: process the signaling control part, transmit IP bearer informationsuch as the IP address and the port number by extended BSSAP signaling,receive the call request message transmitted by the MS, extractinformation about the code type in the call request message, find theintersection with the code types it supports, and establish the prioritylist of the code type; transmit a message to the MS indicating that thecall is being processed, transmit a message to the MGW for adding awireless side end point, and receive the response message returned bythe MGW; transmit or receive a message carrying the priority list of thecode type information to or from other MSC servers, and accomplish codetype negotiation for realizing TrFO; transmit an assignment message tothe BSC, and receive an assignment response message containinginformation about the selected code type transmitted from the BSC;perform code type negotiation and transmit a bearer and code type modifymessage to the MGW, where the bearer and code type modify messagecarries the IP address and the port number information assigned for thecall by the BSC; and distribute the message for changing the code typeto the BSC or the MGW as necessary, if the code type conversion functionis realized at the BSC.

The MGW is configured to: establish an IP bearer with the BSC andperform code type conversion, receive a message for adding a wirelessside end point transmitted by the MSC server, transmit the responsemessage containing the IP address and the port number assigned for thecall to the MSC server, receive the bearer and code type modify messagetransmitted by the MSC server, acquire the IP address and the portnumber assigned for the call by the BSC, and establish an IP bearer;modifies the code type for the corresponding end point as instructed bythe message.

In the system shown in FIG. 3, the MGW(s) may be a same MSW or may bedifferent MGWs. When the MGWs are different MGWs, the process ofestablishing the IP bearer connection for the A interface between theBSC on the other side and the MGW is similar to that of the system shownin FIG. 3, and the description of the process will not be repeated.

Also, the MSC server(s) may be a same MSC server or may be different MSCservers. When the MSC servers are different MSC servers, an Nc interfaceis used between the MSC servers and an Nb interface is used between theMGWs. The MSC server at the calling side transmits initialization (IAM)information to the MSC server at the called side, and the MSC server atthe called side returns IP bearer information to establish an IP bearerbetween the Nb interface side of the MGW at the calling side and the Nbinterface side of the MGW at the called side. The BICC and the IP BearerControl Protocol (IPBCP) may be referred to for details. The process ofestablishing the IP bearer connection between the wireless side of theMGW and the BSC on both the calling side and the called side is similarto the process of establishing the IP bearer connection between thewireless side of the MGW and the BSC on either the calling side or thecalled side, in which code type negotiation is required for theestablishment of TrFO and the establishment of the IP bearer. Thedifference is that: if both sides are IP bearers, a full path TrFOnegotiation for voice channel is required to be performed; but if onlyone side is an IP bearer, only a voice channel with half path TrFO maybe established.

In FIG. 3, the assignment response message should include informationsuch as information about the code type selected by the BSC, the IPaddress and the port number assigned for the call by the BSC.

In practical applications, alternatively, code type negotiation andmodifying may be performed after the establishment of the IP bearer bythe BSC with the MGW. The specific process is described as follows.

First, base station control devices such as the BSC remove the TRAUencapsulation (i.e., the processing of TRAU termination) of the receivedwireless side data to obtain payload data after voice compressioncoding. After that, the payload data after voice compression coding isencapsulated in IP packets, passed to the MGW via the A interfacebetween the BSC and the MGW. The MGW continues to perform servicetransmission processing.

In the implementation of the process of removing TRAU encapsulationdescribed above, the voice compression coding method of the currentframe may be obtained according to a certain bit in it. After that, thedata is subject to corresponding processing according to the acquiredcoding method. For example, for the FR coding method, an FR voice of 20ms has exactly 260 bits and D1 through D260 are the final voicecompression coded payload data. For the EFR coding method, the non-EFRcoded voice data for Cyclic Redundancy Check (CRC) in the 260 bits needto be removed to obtain the final 244 bits of data corresponding to theEFR voice of 20 ms, and so on.

In practical applications, after the MGW receives the voice compressioncoded payload data (i.e., payload data after compressed coding)transmitted via IP packets by the BSC, at least one of the following twotreatments may further be carried out:

(1) determining whether the compression coding method used for the voicecompression coded payload data is the same as the compression codingmethod used on the receiving end side of the data (the Nb interface orthe A interface on the other side); and

(2) determining whether the encapsulation method used for the voicecompression coded payload data is the same as the encapsulation methodused on the receiving end side of the data.

In the determinations described above, if the determination result ispositive, the data is directly passed to the receiving end of the data.Otherwise, at least one of the compression coding method and theencapsulation method of the data that is determined to be different isconverted into the compression coding method and/or the encapsulationmethod used on the receiving end side and then transmitted to thereceiving end.

In order for the MGW to be able to identify and determine thecompression coding method used for the voice compression coded payloaddata, the corresponding processing may be as follows. First, the BSCtransmits the compression coding method used for the received voicecompression coded payload data to the MSC server. After that, the MSCserver transmits the compression coding method used for the data to theMGW, so that the MGW knows the corresponding compression coding method.

Furthermore, in order for the MGW and BSC to learn the bearerinformation of the received data, the bearer information used for thetransmitted data may also be transmitted to the MSC server by the BSC,and transmitted by the MSC server to the MGW. The bearer informationused for the transmitted data may alternatively be transmitted to theMSC server by the MGW, and transmitted by the MSC server to the BSC.

The service transmission processes provided in embodiments of thepresent invention includes a service transmission process in the SecondGeneration Mobile Communication System and a service transmissionprocess between the Second and the Third Generation Mobile CommunicationSystems, which will be described respectively in the following.

In the Second Generation Mobile Communication System, for single ratecoding, service transmission between the MGW on the calling user sideand the MGW on the called user side is not realized with a user planeencapsulation method. In other words, the user plane encapsulationoperation is not conducted at the MGW.

In the Second Mobile Communication System and the Third GenerationMobile Communication System, if a single rate coding is used between theMGW at the calling user side and the MGW at called user side, servicetransmission between the two MGWs is not realized with the user planeencapsulation method. In other words, the user plane encapsulationoperation is not conducted at the MGW. If a multiple rate coding isused, the service transmission is realized with the user planeencapsulation method. In other words, corresponding user planeencapsulation operation needs to be carried out at the MGW.

In the processing described above, a Real-time Transmission Protocol(RTP) encapsulation method is used for the service transmission betweenthe BSC and the MGW.

An example is as follows, in which the Abis interface between the BTSand the BSC is a TDM bearer. At the BSC, only the conversion from TDMbearer to IP bearer and the termination of TRAU, i.e., the processing ofremoving TRAU encapsulation, are performed, without transcoding. Inother words, transmitted between the BSC and the MGW are the GSMcompression coded data. The corresponding compression coding method maybe HR coding, FR coding, EFR coding or AMR (adaptive rate) coding. Inthe BSC, the GSM compressed coded voice payload is encapsulated as RTPmessages and transmitted to the MGW. No codec conversion TC needs to beremained any longer in the BSC.

FIG. 4 is a diagram illustrating the architecture of the BSC accordingto an embodiment of the present invention. Referring to FIG. 4, the BSCincludes:

a receiving unit, configured to receive an assignment message andtransmit the assignment message to a processing unit;

a processing unit, configured to receive the assignment message, acquirethe IP address and the port number of the wireless side end point of theMedia Gateway contained in the message, assign the IP address and theport number for a call, initiate the establishment of an IP bearer, andtransmit an assignment response message containing the IP address andthe port number assigned for the call by the equipment to a transmittingunit; and

a transmitting unit, configured to receive and transmitting theassignment response message.

After receiving the assignment message, the processing unit may furtherselect a code type according to the priority order in a priority list ofthe code type or a preset policy and transmit the selected code type inthe assignment response message to the MSC server via the transmittingunit.

In practical applications, the BSC may also be configured to remove theTRAU encapsulation of the received wireless side data to obtain thevoice compression coded payload data and encapsulate the voicecompression coded payload data in IP packets. It may also be configuredto transmit information about the compression coding method used fortransmitting data in user plane and/or bearer information to the MSCserver and the MSC server transmits information about the compressioncoding method and/or the bearer information of the data to the MGW. Atthe same time, it may also receive information about the compressioncoding method and/or the bearer information transmitted by the MGW viathe MSC server.

FIG. 5 is another diagram illustrating the architecture of the BSCaccording to an embodiment of the present invention. Referring to FIG.5, the BSC includes the following units:

(1) a TRAU terminating unit, configured to remove TRAU encapsulationfrom the received wireless side data to obtain the voice compressioncoded payload data;

(2) a data encapsulating unit, configured to encapsulate the voicecompression coded payload data obtained through processing by the TRAUterminating unit into IP packets and transmit it to a first datatransmitting unit; and

(3) a first data transmitting unit, configured to transmit the IPpackets encapsulated by the data encapsulating unit to the MediaGateway.

Optionally, the BSC further includes at least one of a compressioncoding method transmitting unit, a first bearer information receivingunit and a first bearer information transmitting unit.

The compression coding method transmitting unit is configured totransmit information about the compression coding method used for thedata transmitted in user plane to the MSC server.

The first bearer information receiving unit is configured to receive thebearer information used for the data passed by the MGW from the MGW viathe MSC server.

The first bearer information transmitting unit is configured to transmitthe bearer information used for the data transmitted in user plane tothe MSC server.

In practical applications, the Transcoder and Rate Adoption Unit, theterminating unit and the data encapsulating unit may also be included inthe processing unit as sub-units of the processing unit.

In practical applications, the processing unit may further include acode converting module for converting code types according to the codechange message distributed by the Mobile Switching Center Server.

FIG. 6 is a diagram illustrating the architecture of the MGW accordingto an embodiment of the present invention. Referring to FIG. 6, the MGWincludes:

a receiving unit, configured to receive a message for adding a wirelessside end point, receive a bearer and code type modify message, andtransmit them to a processing unit;

a processing unit, configured to receive the message for adding awireless side end point, assign an IP address and a port number for acall, output a response message containing the IP address and the portnumber assigned for the call to a transmitting unit; receive the bearerand code type modify message, acquire the IP address and the port numberassigned for the call by the BSC, and establish the IP bearer with theBSC; and

a transmitting unit, configured to receive and transmitting the responsemessage.

In practical applications, the MGW may farther be configured to continuethe transmitting of IP packets carrying voice compression coded payloaddata with TRAU encapsulations removed after acquiring IP packets via theA interface between the base station control device and the MediaGateway. It may further communicate with the MSC server to acquire thecompression coding method information from the MSC server which isreceived from the BSC and learn the corresponding compression codingmethod. And, it transmits the bearer information used for the locallytransmitted data to the MSC server to transmit the bearer information tothe BSC via the MSC server. That is, it reports the bearer informationassigned for the call by the MGW at the wireless side end point to theMSC server, and the bearer information is then distributed to the BSC toallow each of the MGW and the BSC to establish a bearer between themafter acquiring the bearer information from each other.

FIG. 7 is another diagram illustrating the architecture of the MGWaccording to an embodiment of the present invention. Referring to FIG.7, the MGW may include the following units:

(1) a data receiving unit, configured to receive the voice compressioncoded payload data contained in IP packets transmitted via the Ainterface;

(2) a conversion processing unit, configured to convert the compressioncoding method and/or the encapsulation method of the data in the IPpackets into the compression coding method and/or the encapsulationmethod used on the receiving end side, and then incorporate the data inIP packets, i.e., perform corresponding conversion processing betweentwo sides of the MGW; and

(3) a second data transmitting unit, configured to transmit the IPpackets processed by the conversion processing unit to the MGW where thereceiving end of the data is.

Optionally, the MGW may further include a determination processing unitfor determining whether the compression coding method and/orencapsulation method used for the data in the IP packets are the same asthe compression coding method and/or encapsulation method used on thereceiving end side of the data. If the compression coding methods and/orencapsulation methods are the same, the IP packets are directlytransmitted to the data transmitting unit. Otherwise, the IP packets aretransmitted to the conversion processing unit. That is, the MGW mayselect to determine at least one of the compression coding method andthe encapsulation method used for corresponding data between two sidesof the MGW to perform a corresponding conversion processing according tothe determination result.

Optionally, the MGW may further include at least one of a compressioncoding method receiving unit, a second bearer information transmittingunit and a second bearer information receiving unit.

The compression coding method receiving unit is configured to receivefrom the MSC server the compression coding method used for the datatransmitted in user plane by the BSC and provide the compression codingmethod to the compression coding method determining unit.

The second bearer information transmitting unit is configured totransmit the bearer information used for the data transmitted by the MGWto the MSC server to transmit the bearer information to the BSC via theMSC server.

The second bearer information receiving unit is configured to receivefrom the MSC server the bearer information used for the data transmittedby the BSC in user plane and provide it to the data transmitting unit.

Optionally, the MGW may further include a bearer information negotiatingunit for negotiating bearer information used during data transmissionwith the MGW at the opposite end.

FIG. 8 is a diagram illustrating the architecture of the MSC serveraccording to an embodiment of the present invention. Referring to FIG.8, the MSC server includes:

a receiving unit, configured to receive a call request containinginformation about the code types supported by itself transmitted by theMS, a response message containing the IP address and the port numberassigned for the call returned by the MGW wireless side end point and anassignment response message returned by the BSC, and transmit them tothe processing unit;

a processing unit, configured to establish a priority list of the codetype according to the call request message, transmit to the transmittingunit a message for adding a wireless side end point; generate anassignment message according to the received response message and thepriority list of the code type, and output it to the transmitting unit;conduct code type negotiation according to the received assignmentresponse message and output a bearer and code type modify messagecontaining information on the IP address and the port number assigned tothe call by the Base Station Controller to the transmitting unit; and

a transmitting unit, configured to receive and transmit to the MGWwireless side end point the message for adding a wireless side end pointand the bearer and code type modify message containing information onthe IP address and the port number assigned for the call by the BaseStation Controller which is output by the processing unit; and receivethe assignment message output by the processing unit and transmit it tothe BSC.

Based on the system shown in FIG. 3, seven embodiments are illustratedbelow to describe in detail specific implementations of applications ofthe present invention during the implementation of the GSM network withIP-based interfaces. In the diagrams showing system structures of theseven embodiments of the present invention, broken lines denotesignaling information and solid lines denote bearer information.

Embodiment 1

FIG. 9 is a diagram illustrating the structure of the GSM network withan IP-based A interface in the first embodiment of the presentinvention. By taking BTS, BSC, MSC server and the MGW included on thecalling side as an example, the present embodiment illustrates that thetranscoding TC is arranged on the BSC side and the A interface isIP-based. The IP-based A interface on the called side is similar to thaton the calling side and will not be described in detail. Referring toFIG. 9, the interface between the BTS and the BSC is an Abis interface,and the interface between the BSC and the MGW is an A interface. On theside of the MGW where the MGW is connected with the BSC is the MGWwireless side end point. The interface between the MGW and the MSCserver is an Mc interface.

The A interface control plane is based on the Signal Transmission(Sigtran) protocol specified in standards. In the present embodiment, inorder to realize the IP-based A interface, it is required to extend thefunction of the management of the IP-based voice resources of the Ainterface control plane and to extend necessary BSSAP information. Forexample, the extended BSSAP message has the ability to transmit IPbearer information such as IP addresses and port numbers.

The MS initiates a call containing information on code types supported,which is transmitted transparently via the BTS. The BSC receives thecall request message and transmits it to the MSC server via BSSAPsignaling. The MSC server acquires information about the code typessupported by the calling side, finds the intersection with the codetypes supported by the MSC server, and forms a priority list of the codetype. The MSC server transmits a message for adding a wireless side endpoint to the MGW via the Mc interface. The MGW receives the message foradding a wireless side end point, assigns an IP address and a portnumber for the call, and returns a response message for the IP addressand the port number assigned for the call by the MGW to the MSC servervia the Mc interface. The MSC server receives the response message fromthe MGW. The MSC server transmits the assignment message containing theIP address, the port number assigned for the call by the MGW and thepriority list of the code type of the MSC server to the BSC via BSSAPsignaling. The BSC receives the assignment message, assigns the IPaddress and the port number of its own side for the call and initiatesthe establishment of the IP bearer. At the same time, the BSC selectscode types according to the priority list of the code type informationor its own policy, and returns an assignment response message containinginformation about the code type selected by the BSC and the IP addressand the port number assigned for the call by the BSC to the MSC server.The MSC server receives the assignment response message, acquires fromthe message the IP address and the port number assigned for the call bythe BSC and transmits a bearer and code type modify message to the MGWwireless side end point. The MGW wireless side end point may establishan IP bearer with the BSC once it acquires the IP address and the portnumber assigned for the call by the BSC. At the same time, the MSCserver receives the assignment response message, acquires the code typeselected by the BSC from the message, places the code type selected bythe BSC on the calling side at the first position in the priority listof the code type and then transmits the priority list of the code typeto the MSC server on the called side. In the backward transmissionprocess, the code types of the end points related to the MGWs in thepath is indicated or changed to the optimum code type, namely the codetype selected by the BSC. The MSC server on the called side distributesthe acquired priority list of the code type to the BSC on the calledside. If the BSC on the called side supports the code type selected bythe BSC on the calling side, and selects the optimum code type, a fullpath TrFO voice channel is realized. Otherwise, the BSC on the calledside feeds back the selected code type to the MSC server on the calledside with an assignment response message. The MSC server on the calledside then distributes a message for changing the code type to the BSC onthe called side or to the BSC on the calling side via the MSC server onthe calling side. The BSC on the called side, the MGW on the calledside, the BSC on the calling side or the MGW on the calling sideconducts conversion between the code type selected on the calling sideand that selected on the called side after receiving the message forchanging the code type.

If between the MGW on the called side and the BSC on the called side isa TDM bearer, and the BSC on the called side supports the code typeselected by the BSC on the calling side and selects the optimum codetype, the MSC server on the called side distributes a bearer formatconversion message to the MGW on the called side on which a bearerformat conversion from IP to TDM is accomplished. Here, the MSC serveron the called side returns the negotiated code type to the MSC server onthe calling side and TrFO may be realized on the called side. Otherwise,if the BSC on the called side does not support the code type selected bythe BSC on the calling side, the MSC server on the called side selectsone code type from the code types supported by the BSC on the callingside according to certain rules, returns the selected code type to theMSC server on the calling side and distributes the selected code type tothe MGW on the called side with a code type modify message. The codetype conversion and the bearer format conversion from IP to TDM areachieved at the same time at the MGW on the called side. Similarly, ifbetween the MGW on the calling side and the BSC on the calling side is aTDM bearer, the code type conversion and the bearer format conversionfrom IP to TDM are achieved at the same time at the MGW on the callingside. However, the code type negotiation processes between MSC serversare different. The MSC server on the calling side indicates that thecode type selected by the BSC on the called side should be returned inthe message sent to the MSC server on the called side. Therefore the MSCserver on the called side passes information about the code typeselected by the BSC on the called side to the MSC server on the callingside and modifies the code types of the end points related to the MGW inthe path into the code type selected by the BSC on the called side. Thenthe MSC server on the calling side distributes information about thecode type selected by the BSC on the called side to the end points ofthe Nb interface of the MGW on the calling side, namely end points onboth sides of the core network. Thus it is ensured that code types arethe same for all IP bearer parts and TC is inserted into only the TDM toIP conversion point.

FIG. 10 is a diagram illustrating the hierarchical structure of theprotocol stack of the signaling plane and the bearer plane of the Ainterface of the system shown in FIG. 9 according to the embodiment ofthe present invention. Referring to FIG. 10, the bottom layer of the Ainterface signaling plane protocol stack is a Media Access Control (MAC)layer. If the protocol of the physical layer is not a hundred-megabit orgigabit Ethernet but a Packet Over SONET/SDH/GE (Gigabit Ethernet) (POS)point-to-point protocol or IP over E1, the bottom layer is aPoint-to-Point Protocol (PPP) layer. From here tip, the second layer isan IP layer, the third layer is a Stream Control Transmission Protocol(SCTP) layer, the fourth layer is an M3 User Adaptation (M3UA) layer,the fifth layer is a Skinny Client Control Protocol (SCCP) layer and thetop layer is a BSSAP layer. Signaling is transmitted sequentially amongthe layers. In the present embodiment, the BSSAP protocol of the BSSAPlayer and the function of the management of the IP-based voice resourcesneed to be extended accordingly.

If the IP interface is a hundred-megabit or gigabit Ethernet, the bottomlayer of the A interface bearer plane protocol stack is an MAC layer. Ifthe IP interface is a POS interface or an IP over E1 interface, thebottom layer is a PPP layer. From here up, the second layer is an IPlayer, the third layer is a User Data Protocol (UDP) layer, and thefourth layer is a Real-time Transmission Protocol (RTP) layer. Thebearer information is transmitted sequentially among the layers.

In practical applications, voice frames based on IP protocol may also betransmitted by changing the original TDM bearer of the Abis interfacebetween the BTS and the BSC to an IP bearer. This can further lower thetime delay caused by the network bearer conversion and increaseutilization ratio of the transmission resources.

Also, MSC servers at the calling and called side in the embodiment maybe a same MSC server or may be different MSC servers. When the MSCservers are different MSC servers, after acquiring the code typeselected by the corresponding BSC, the MSC server on one side negotiatescoding with the MSC server on the other side. If there is no anyconsistent code type which both the two sides accept, TC is insertedonly in the BSC on one side for transcoding.

As seen from the above-described embodiments of the present invention,an IP bearer is established at the A interface between the BSC and theMGW through the MSC server, which effectively decreases the number ofconversions of voice coding formats and even eliminates the necessity ofsuch a conversion, decreases the delay of voice transmission, increasesthe quality of voice transmission and saves TC resources. At the sametime, since an IP bearer is used, valuable long-distance transmissionresources between the BSC and the MGW are saved. For example, in theexisting GSM network system, tip to 4 TCs are required between the BSCson the calling and called sides for the conversion of different codetypes and bearers. After the IP bearer is established at the Ainterface, no or only 1 TC is required between the BSCs on the callingand called sides for the conversion of code types and no bearerconversion is needed. If the Abis interface is further changed to be IPbearer, no bearer conversion is needed along the entire call pathbetween the MSs on the calling and called sides.

In the first embodiment described above, TCs are disposed on the BSCside. In practical applications, TCs may alternatively be disposed onthe MGW side and an IP bearer is implemented for the A interface. In thecase that TCs are disposed on the MGW side, TRAU frames may beterminated at the BSC side or at the MGW side. Specific implementationswill be explained below in connection with the second and thirdembodiments respectively.

Embodiment 2

FIG. 11 is a diagram illustrating the structure of a GSM network with anIP-based A interface in the second embodiment of the present invention.In the present embodiment, the BTS, BSC, MSC server and the MGW includedon the calling side are taken as an example. The MSC servers and theMGWs on the calling side and the called side may be the same MSC serverand the same MGW, respectively. TCs are disposed on the MGW side andTRAU frames are terminated at the BSC side. That is, between the BSC andthe MGW is an A interface which realizes IP bearer, and theencapsulation and transmission of services to be transmitted arerealized using an IP-based encapsulation method between the BSC and theMGW. For example, services to be transmitted such as compression codedvoice services are encapsulated in IP messages, IP-based User DataProtocol messages or IP-based RTP messages.

The A interface control plane is based on the Sigtran protocol bearerspecified in standards. The resources management function of the IPvoice bearer needs to be extended. The BSSAP information is extended toenable the extended BSSAP information to transmit IP bearer informationsuch as IP addresses and port numbers. The A interface service planeutilizes an IP bearer.

The establishment of IP bearer connection at the A interface of thesystem shown in FIG. 11 is similar to that of FIG. 9 with the differencethat code type conversions are all performed at the MGW instead of theBSC. After the BSC selects a code type, the BSC incorporates theinformation on the code type selected by the BSC into the assignmentresponse message of the MSC server via BSSAP signaling and the MSCserver is in charge of code type negotiation. If the BSC on the calledside supports the code type selected by the BSC on the calling side, andthe optimum code type is selected, TrFO of the voice channel isrealized. Otherwise, the MSC server on the called side receives theassignment response message of the BSC on the called side anddistributes the code type selected by the BSC on the called side to theMGW wireless side end point on the called side via a code type modifycommand through the Mc interface. Alternatively, the MSC server on thecalled side forwards the code type selected by the BSC on the calledside to the MSC server on the calling side. The MSC server on thecalling side distributes the code type selected by the BSC on the calledside to the Nb side end point of the MGW on the calling side via a codetype change command. After receiving the command, the MGW compares thecode type with that selected by the BSC on the calling side. If they arenot the same, TCs are inserted.

The hierarchical structure of protocol stack on the A/Ater interfacesignaling plane is the same as that shown in FIG. 10.

If only one side of the A interface on the calling/called sides isIP-based while the other side is of TDM, the code type conversion alwaysoccurs at the MGW of which the A interface is of TDM. The specificimplementation is similar to that of the first embodiment.

Similarly, the original TDM bearer at the Abis interface between the BTSand the BSC may also be replaced with an IP bearer to further reduce thetime delay caused by network bearer conversion and increase utilizationratio of transmission resources.

In the case that TCs are disposed on the MGW side and TRAU frames areterminated on the BSC side, an embodiment of the present invention alsoprovides detailed implementation solutions for the A interface, Nbinterface and Mc interface, which will be described one by one below.

I. Voice Protocol Stack at the A interface

FIG. 12 is a diagram illustrating the voice message encapsulationstructure at the Abis interface according to the second embodiment ofthe present invention. Referring to FIG. 12, no matter whether the Abisinterface is based on IP or TDM, the TRAU in the BSC uniformlyencapsulates voice messages at the Abis interface into an RTPencapsulation format without any user plane (UP), which includes frombottom to top an MAC or PPP protocol layer, an IP layer, an UDP layer,an RTP layer and a payload layer.

The corresponding bottom layer is an MAC layer for an FE (Fast Ethernet)or a GE (Gigabit Ethernet) interface and is a PPP layer for a POS and IPover E1 interface.

For a coding method of EFR, FR or HR, the Payload layer of thecorresponding top layer bears the payload of the voice messages. For itsspecific byte order encapsulation format, the encapsulation methoddefined in the European Telecommunications Standards Institute (ETSI)standard (ETSI ts_(—)101318) may be used. For the AMR coding method,since it is a variable rate voice coding with a process of adjustingin-band voice rate, the encapsulation method defined in the InternetEngineering Task Force Request For Comments (IETF RFC3267) standard isused for the corresponding Payload layer.

In embodiments of the present invention, to be in accordance with TRAU,the packet time for voice service may be uniformly set as 20 msspecifically.

Taking GSM as an example, the coding methods often used include EFR, FR,HR or AMR. Each of the clock rates for EFR and FR is 8000 Hz. ThePayload Type (PT) for FR is a static 3. The PT for EFR is dynamic(96-127).

In the case of FR coding method, corresponding processing is relativelysimple due to the static PT.

In the case of EFR coding method, due to the PT of EFR coding for Ainterface, the BSSAP signaling needs to be extended so that the PT ofEFR between the BSC and the MGW is negotiated between the MSC server andthe BSC. Alternatively, the corresponding PT is preconfigured at the MSCserver and then distributed to the BSC and the MGW via the BSSAP messageand the Mc message. Alternatively, the corresponding PT (with its valueranging 96-127) is determined by configurations on the BSC and the MGWand it is enough to keep both sides the same.

For other coding methods such as HR, it may be implemented withreference to the PT determining method described above, for example,being consistent with EFR or using a dynamic PT, for which detaileddescription is omitted.

Definitions of PT values corresponding to different coding methods anddata services may be the following values specifically:

-   -   FR: 3;    -   EFR: 96-127;    -   HR: 96-127;    -   AMR: 96-127;    -   DATA(data service): 96-127;    -   RED(redundancy): 96-127;

For each of the EFR, HR, AMR or data services, the data redundancies areall dynamic PTs with specific values collectively distributed to the MGWand the BSC by the MSC server.

Corresponding PTIME (packet time): 20 ms.

DTX (Discontinuous transmission): Both the BSS and the MGW need support.

II. Implementation of the Mc Interface

The MSC server provides the bearer information of the A interface to theMGW via the Mc interface.

Specifically, the BSC reports its own bearer information such as the IPaddress and the port number to the MSC server via the extended BSSAPmessage, and the MSC server distributes the bearer information from theBSC and the code type negotiation result to the MGW. At the same time,the MSC server further receives the bearer information of MGWtransmitted from the MGW and distributes it to the BSC.

For different coding methods, the SDP (Session Description Protocol)message of the bearer information distributed by the MSC server isdefined as follows:

(1) FR coding

-   -   c=IN IP4 10.10.10.1;    -   m=audio 49120 RTP/AVP 3:    -   a=ptime:20;

Where c refers to the connection information, m refers to the media nameand the transmission address and a=ptime refers to the packet time.

(2) EFR coding

-   -   c=IN IP4 10.10.10.1;    -   m=audio 49120 RTP/AVP 98:    -   a=rtpmap:98 GSM-EFR/8000;    -   a=ptime:20;    -   Where a=rtpmap refers to the media attribute lines, namely        coding name.

(3) HR coding

-   -   c=IN IP4 10.10.10.1;    -   in=audio 49120 RTP/AVP 98;    -   a=rtpmap:98 GSM-HRW8000;    -   a=ptime:20;

(4) AMR coding

-   -   See detailed definition in RFC3267.    -   c=IN IP4 10.10.10.1:    -   m=audio 49120 RTP/AVP 97;    -   a=rtpmap:97 AMR/8000/1;    -   a=fmtp:97 mode-set=0,2,5,7;    -   a=maxptime:20;

(5) Data service

-   -   c=IN IP4 10.10.10.1;    -   m=DATA 49120 RTP/AVP 97;

SERVER ensures that the above PTs are different from each other.

III. Implementation of the Nb interface

The corresponding PT is negotiated by the Nb interface using the IPBCP.

To realize TRFO, the processing at the Nb interface should be keptconsistent with that at the A interface as much as possible. For a 2 Gto 2 G call, the encapsulation method without UP is used whether it is asingle rate coding or a multiple rate coding. For a 2 G to 3 G call, anencapsulation method consistent with that at A interface is used forsingle rate coding and an encapsulation method with UP is used in thecase that both 2 G and 3 G use the AMR coding.

(1) Calling procedure for single rate coding/decoding

FIG. 13 is a diagram illustrating a 2 G to 2 G calling procedureaccording to the second embodiment of the present invention. Referringto FIG. 13, the call from BSC1 to BSC2 is an intra-office call and thecall from BSC1 to BSC3 is an inter-office call. Whether intra- orinter-office call, the UP encapsulation method is not used for singlerate coding/decoding (HR/FR/EFR). Instead, a mode in which voicemessages are directly encapsulated with RTP messages is used.

FIG. 14 is the first diagram illustrating the architecture of the userplane protocol stack at the Nb interface according to the secondembodiment of the present invention. Referring now to FIG. 14, which isa single rate coding payload encapsulation method corresponding to FIG.13. There are from bottom to top: an MAC or PPP protocol layer, an IPlayer, an UDP layer, an RTP layer and a Payload layer. The Payload layermay include data of HR, FR or EFR coding method specifically.

(2) Multiple rate coding/decoding

FIG. 15 is a diagram illustrating a networking structure of interworking2 G and 3 G according to the second embodiment of the present invention.FIG. 16 is the second diagram illustrating the architecture of the userplane protocol stack at the Nb interface according to the secondembodiment of the present invention. Referring now to FIG. 15, whichshows also a 2 G to 2 G call between BSC1 and BSC2. When the AMRcoding/decoding is adopted, the corresponding encapsulation format isthe encapsulation method specified by the RFC3267 shown in FIG. 16rather than the UP encapsulation format.

The call between BSC1 and RNC1 and the call between RNC2 and BSC2 inFIG. 15 are 2 G to 3 G calls. For a 2 G to 3 G call, in the case thatAMR coding/decoding is used, the corresponding UP encapsulation methodis shown in FIG. 17. FIG. 17 is the third diagram illustrating thearchitecture of the user plane protocol stack at the Nb interfaceaccording to the second embodiment of the present invention. Differentfrom FIG. 16, the AMR Payload in FIG. 17 is the payload of AMR. When thesubscriber of 2 G is the calling party, the UP direction at the Nbinterface close to 2 G side is CN/Outgoing (outgoing direction of thecore network). When the subscriber of 2 G is the called party, the UPdirection at the Nb interface close to 2 G side is CN/Incoming (incomingdirection of the core network). That is, the MGW on the 2 G side isrequired to accomplish the conversion from the AMR encapsulation methodwithout UP (A interface) to the AMR encapsulation method with UP.

After the A interface becomes IP-based, if the inter-office Nb interfaceuses the AMR mode with UP, the bearer information at the Nb interfacefor negotiation at the Nb interface with the IPBCP is as follows:

-   -   c=IN IP4 1 92.168.153.21;    -   m=audio 764 RTP/AVP 96:    -   a=ptime:20;    -   a=rtpmap:96 VND.3GPP.IUFP/16000.

After the A interface becomes IP-based, if the Nb interface does not usethe AMR mode with UP, the IPBCP negotiation may be subject to but notlimited to the following extensions respectively according to codingmethods and data service types:

(1) For a 2 G to 2 G call, if the inter-office Nb interface uses AMRwithout UP of RFC3267 method, the bearer information negotiated with theIPBCP is:

-   -   c=IN IP4 192.168.153.21;    -   m=audio 764 RTP/AVP 96;    -   a=ptime:20;

a=rtpmap:96 AMR/8000/1;

(2) If RF coding is used between offices, with its PT being a static PT,the bearer information negotiated with the IPBCP is:

-   -   c=IN IP4 192.168.153.21;    -   m=audio 764 RTP/AVP 3;    -   a=ptime:20;

(3) If EFR coding is used between offices, the PT is a dynamic PT andthe bearer information negotiated with the IPBCP is:

-   -   c=IN IP4 192.168.153.21;    -   m=audio 764 RTP/AVP 97;    -   a=ptime:20;    -   a=rtpmap:96 GSM-EFR 8000;

(4) If HR coding is used between offices, the PT is a dynamic PT and thebearer information negotiated with the IPBCP is:

-   -   c=IN IP4 192.168.153.21;    -   m=audio 764 RTP/AVP 97;    -   a=ptime:20;    -   a=rtpmap:96 GSM-HR 8000;

(5) For an inter-office data service with UP of 5 ms, the bearerinformation negotiated with the IPBCP is:

-   -   c=IN IP4 192.168.153.21;    -   m=audio 764 RTP/AVP 96:    -   a=ptime:5;    -   a=rtpmap:96 VND.3GPP.IUFP/16000;

(6) For an inter-office G.711 data service of 20 ms, the bearerinformation negotiated with the IPBCP is:

-   -   c=IN IP4 192.168.153.21;    -   in=audio 764 RTP/AVP 0;    -   a=ptime:20;

or:

-   -   c=IN IP4 192.168.153.21;    -   m=audio 764 RTP/AVP 8;    -   a=ptime:20.

It should be noted that the specific IP address and the port numberinformation in the SDP information above are only examples and may varyin practical applications. If the load type PT information of the RTP isdynamic PT in range of 96˜127, it may vary similarly in practicalapplications.

In embodiments of the present invention, the data encapsulation formatat the Nb interface may specifically be the following. For 2 G to 2 Gdata services, 20 ms packaging is used and the mode of RFC2198 standardis used for redundancy. For 2 G to 3 G data services, the G.711encapsulation method with UP of 5 ms is used.

Embodiment 3

FIG. 18 is a diagram illustrating the system structure for theimplementation of the IP-based Ater interface in the GSM networkaccording to the third embodiment of the present invention. FIG. 18 isdifferent from FIG. 11 in that, the TRAU frames transmitted by thesystem shown in FIG. 18 are terminated at the MGW side. In other words,the interface between the BSC and the MGW corresponds to the Aterinterface in the original GSM system.

Since TRAU frames are terminated at the MGW side, the interface betweenthe BSC and the MGW is an Ater interface. And the A interface in theoriginal GSM system has shrunk into inside the MGW. Sigtran bearer isused for the A interface signaling. IP bearer mode is used for the Aterinterface signaling. Signaling between the BSC and the MSC server may becommunicated directly via IP or may be forwarded via IP by the MGW.There are two ways for the MSC server to control the establishment ofthe circuit of the IP bearer plane of the Ater interface:

(1) The MSC server does not control the establishment of the circuit ofthe IP bearer plane of the Ater interface. With the in-band signalingmode of the bearer plane, the MGW and the BSC negotiate to establish anAter interface channel via TRAU signaling. The MGW acquires the voicecode type of the BSC by resolving the TRAU frames of the Ater interfaceand compare it with the code type of core network. If the code types arenot consistent with each other, a TC is inserted for conversion of voicecoding.

(2) The MSC server controls the establishment of the circuit of the IPbearer plane of the Ater interface. The resource management function ofIP voice bearer mode and information related to the IP bearer of theBSSAP protocol are extended and the Ater interface is simulated as an Ainterface in the original system. The establishment of the circuit ofthe IP bearer plane of the Ater interface is similar to that of FIG. 9.The difference lies in that, after the MGW and the BSC establish IPbearer, the MSC server acquires the code type selected by the BSC andthen distributes it to the end point of the MGW corresponding to the BSCside, hence ensuring that the code type on the BSC side is consistentwith the code type of the end point of the MGW corresponding to the BSC.Then the MGW compares code types on both sides for consistence. If theyare consistent, TrFO of voice channel is realized. Otherwise, a TC isinserted for transcoding.

Compared with FIG. 10, the fifth TRAU layer is added in the protocolstack of the A/Ater interface bearer plane of the system shown in FIG.18.

As can be seen from the above-described embodiments, neither TRAU frameprocessing nor conversion of voice coding is required at the BSC, onlythe transparent transmission of TRAU frames is performed.

In the first, second and third embodiments described above, thetransmitted TRAU frames are terminated by the BSC or the MGW. Further,TRAU frames may also be canceled throughout the network, that is,IP-based voice frames are output directly at the BTS.

The specific implementations will be described below with the fourth andfifth embodiments respectively.

Embodiment 4

FIG. 19 is a diagram illustrating the structure of the IP-based GSMnetwork according to the fourth embodiment of the present invention. Asshown in FIG. 19, the establishment of IP bearer connection between theBSC and the MGW is similar to that of FIG. 9. The BSSAP protocol needsto be extended as necessary for transmitting IP bearer information suchas the IP address and the port number. If the code type on the MGW sideof the calling side BSC is inconsistent with that on the called side ofthe called side BSC, a TC is inserted on the MGW side for transcoding.After the IP bearer connection is established, the BTS outputs IP-basedvoice frames, such as IP/UDP/RTP/VOICE messages and the BSC receives thevoice frames to forward them to the MGW.

In the above-described embodiment, since bearer mode conversion is notrequired, the time delay of transmission is decreased and the quality ofvoice transmission is enhanced.

Further, in the above-described embodiment, after the IP bearerconnection is established, the BSC may alternatively not participate inthe forwarding of voice frames, and voice frames are communicateddirectly between the BTS and the MGW, which further decreases the timedelay caused by the voice frames forwarding at the BSC and saves theprocessing capacity of the BSC, which is described specifically in thefifth embodiment.

Embodiment 5

FIG. 20 is a diagram illustrating the structure of the IP-based GSMnetwork according to the fifth embodiment of the present invention. TheBSC communicates signaling with the BTS and the MSC server via asignaling channel such as Link Access Procedure on the D channel (LAPD)and a BSSAP, respectively, and does not participate in the forwarding ofvoice frames on bearer plane. In the present embodiment, in order toestablish the bearer connection between the BTS and the MGW, the BSSAPprotocol and the LAPD protocol need to be extended with respect to IPbearer information. The establishment of the bearer connection issimilar to that of FIG. 9. The difference is as follows. The BSCreceives the assignment message and acquires the IP bearer informationand then transmits it to the BTS via LAPD signaling. The BTS acquiresthe IP address and the port number assigned for the call by the MGWwireless side and assigns the IP address and the port number of its ownside BTS for the call. The BTS reports the IP bearer information (the IPaddress and the port number) assigned for the call to the BSC. The BSCthen transmits the IP address and the port number assigned by the BTScarried in the assignment response message to the MSC server. The MSCserver then indicates them to the MGW. The BTS and the MGW may establishthe bearer if both of them know the IP address and the port number ofeach other. The code type used by the BTS, i.e. the selected code typecarried in the assignment response message by the BSC, is completelycontrolled by the BSC. The MSC server distributes the BTS code typeselected by the wireless side to the MGW to ensure that the code type ofthe wireless side end point of the MGW is always consistent with thecode type used by the BTS. The MSC server conducts code type negotiationfor the full path of the voice channel. If the negotiation succeeds,TrFO is realized. If the negotiation fails, the MGW on the calling sideor the MGW on the called side is selected into which a TC for code typeconversion is inserted.

In practical applications, the MS may also switch among different BTSs.The BSC transmits notifications to the MSC server to notify the MSCserver of the new IP addresses and the port numbers of the BTSs. The MSCserver receives the notifications, distributes notifications forchanging the bearer of the MGW and accomplishes bearer switching.

The sixth and seventh embodiments are set forth below to explain thesignaling control procedure of the present invention.

Embodiment 6

FIG. 21 is a diagram illustrating the signaling procedure of arranging aTC at the BSC side according to an embodiment of the present invention.In the present embodiment, the TC is disposed at the BSC, the BSCconverts voice coding, and the IP bearer connection is established atthe calling party. Referring to FIG. 21, the procedure includes thefollowing steps.

In step 211, the MS initiates a call that is forwarded to the MSC servervia the BTS and the BSC.

In step 212, the MSC server returns a message to the MS, indicating thatthe call request is being processed.

In step 213, the MSC server transmits a message to the MGW for adding awireless side end point.

In steps 211˜-213, the call request message received by the MSC servercontains information about the code types supported by the MS itself. Anintersection between the code types and code types supported by the MSCserver is found to form a priority list of the code type and a wirelessside end point is added at the MGW via the Mc interface.

In step 214, the MGW receives the message for adding a wireless side endpoint and returns a response message.

In this step, the MGW receives the message for adding a wireless sideend point, assigns an IP address and a port number for the call, and theresponse message includes the IP address and the port number assignedfor the call by the MGW.

In step 215, the MSC server receives the response message and transmitsan assignment message to the BSC. The message contains the IP addressand the port number assigned for the call by the MGW and the MSC serverpriority list of the code type.

In step 216, the BSC receives the assignment message, returns anassignment response message containing the assigned IP bearerinformation and the selected code type.

In this step, the BSC receives the response message, acquires the IPaddress and the port number assigned by the MGW for the call, assignsthe IP address and the port number of its own side for the call andinitiates the establishment of the IP bearer at the same time. Selectinga code type by the BSC to be used by itself may be selecting a code typeaccording to the order of priority in the priority list of the code typeprovided by the MSC server or according to its own policy. The BSCreturns an assignment response message to the MSC server which containsthe code type selected by the BSC and the IP address and the port numberassigned by the BSC for the call. The MSC server initiates code typenegotiation for the full voice channel call via the following steps.

The BSC selects a code type and transmits the code type information tothe MSC server. The MSC server passes backwardly the code type selectedby the BSC and places the code type selected by the BSC on the callingside at the first position of the priority list of the code type fordistributing to the BSC on the called side. If the BSC on the calledside supports and selects the code type selected by the BSC on thecalling side, a full path TrFO voice channel may be realized. Otherwise,the code type selected by the BSC on the called side is inconsistentwith the priority order in the MSC server priority list of the codetype, code type conversion needs to be performed at the BSC on thecalled side. For example, the calling party assigns FR/EFR, and the BSCon the calling side selects FR. The MSC server on the calling sidepasses the FR backwardly. The called MS supports HR/FR/EFR. The MSCserver on the called side distributes FR/HR/EFR to the BSC on the calledside. If the BSC on the called side selects FR, then the code typeselected by the BSC on the calling side is consistent with the preferredcode type recommended by the MSC server on the calling side, and a fullpath TrFO voice channel may be realized without inserting any TC forcode type conversion. If the BSC on the called side selects HR which isfed back to the MSC server on the called side via the assignmentresponse message. The MSC server on the called side finds out that TrFOcannot be realized in its own segment through analysis and judgment anddistributes a code type modify message to the BSC on the called side toinstruct the BSC on the called side to implement code type conversionbetween FR and HR.

In practical applications, after the IP bearer connection isestablished, if the BSC needs to change the selected code type due toreasons such as wireless network capacity, the BSC changes the selectedcode type by itself and reports it to the MSC server, and a code typere-negotiation is initiated. The process is similar to the code typenegotiation during the call establishment. The difference is that, thecase in which the MSC server on the called side passes preferred codetype to the MSC server on the calling side may occur. After the codetype of the BSC on one side changes, the TrFO of the full voice channelmay be broken. However, it is possible that the original non-TrFO callbecomes a TrFO call through re-negotiation.

Embodiment 7

FIG. 22 is a diagram illustrating the signaling procedure of arranging aTC at the MGW side according to an embodiment of the present invention.Referring to FIG. 22, the procedure includes the following steps.

In step 221, the MS initiates a call that is forwarded to the MSC servervia the BTS and the BSC.

In step 222, the MSC server returns a message to the MS, indicating thatthe call request is being processed.

In step 223, the MSC server transmits a message to the MGW for adding awireless side end point.

In steps 221-223, the call request message received by the MSC servercontains information about the code types supported by the MS itself, anintersection between the code types and code types supported by the MSCserver is found to form a priority list of the code type and a wirelessside end point is added at the MGW via the Mc interface.

In step 224, the MGW receives the message for adding a wireless side endpoint and returns a response message.

In this step, the MGW receives the message for adding a wireless sideend point, assigns an IP address and a port number for the call, and theresponse message includes the IP address and the port number assigned bythe MGW for the call.

In step 225, the MSC server receives the response message and transmitsan assignment message to the BSC which contains the IP address and theport number assigned by the MGW for the call and the MSC server prioritylist of the code type.

In step 226, the BSC receives the assignment message and returns anassignment response message.

In this step, the BSC receives the assignment message, acquires from theassignment message the IP address and the port number assigned by theMGW for the call, assigns the IP address and the port number of its ownparty for the call and establishes the IP bearer. Selecting a code typeby the BSC used by itself may be selecting a code type according to theorder of priority in the priority list of the code type provided by theMSC server or according to its own policy. An assignment responsemessage containing information about the code type selected by the BSCand the IP address and the port number assigned for the call by the BSCis transmitted to the MSC server.

In step 227, the MSC server receives the assignment response message,acquires the information on the IP address and the port number assignedby the BSC for the call, generates a bearer and code type modify messageand transmits it to the wireless side end point of the MGW.

In step 228, the wireless side end point of the MGW receives the IPbearer information and the code type modify message, performscorresponding processing and returns a response message.

In this step, once the MGW obtains the wireless side IP bearerinformation specified by the BSC, the MGW may initiate the establishmentof bearer to the BSC/BTS on the wireless side. The wireless side endpoint of the MGW receives the code type modify message, modifies thecode type of the end point according to the code type instructed in themessage and returns a response message to the MSC server.

The processing of signaling on the called side is similar to that on thecalling side. The code type of the wireless network side end point ofthe BSC is to be ensured consistent with the code type of the BSC sideend point of the MGW by the code type modify message. The MGW is onlyrequired to compare the code types of the Nb interface and the A/Aterinterface for determining their consistence. If the code types areinconsistent, code type converting TCs are inserted; otherwise, no codetype converting TC is inserted and a full path or half path TrFO voicechannel is realized.

After the IP bearer connection is established, the BSC initiates a codetype change request when code types are required to be changed orswitched. After changing the code types of end points corresponding toall MGWs, the MSC server transmits code type change response message tothe BSC. The BSC changes code types.

In the embodiments of the present invention, by using IP transmissionbetween the BSS and the MSS, the object of saving transmission resourcesmay be achieved with the packet multiplexing feature of IP. In practicalapplications, the transmission efficiency may be further increased withrelevant techniques such as Compressed Real-Time Protocol (CROP),Real-Time Protocol Multiplexing (RTP Multiplex), Point to Point ProtocolMultiplex (PPPMUX) and IP header multiplex.

The objects, technical solutions and advantages of the present inventionare described further in details in connection with the above preferredembodiments. It is understood that exemplary embodiments provided aboveare only preferred embodiments of the present invention and is notintended to limit the scope of the present invention. Any modifications,equivalent replacements and improvements within the principle of thepresent invention should be contained in the scope of the presentinvention.

1. A method for establishing a bearer for a GSM network, comprising:receiving, by a Media Gateway, MGW, a message for adding a wireless sideend point, assigning an IP address and a port number for a call, andtransmitting a response message comprising the IP address and the portnumber assigned for the call; and acquiring, by the MGW, an IP addressand a port number assigned for the call by a wireless side Base StationSubsystem, BSS, and establishing an IP bearer with the wireless sideBSS.
 2. The method of claim 1, wherein before receiving the message foradding a wireless side end point, the method further comprises:receiving, by a Mobile Switching Center, MSC, server, a call requestmessage transmitted by a mobile station; and transmitting, by the MSCserver, to the MGW the message for adding a wireless side end point. 3.The method of claim 2, wherein the call request message containinginformation about code types is supported by the mobile station itself;and after receiving the call request message transmitted by the mobilestation, the method further comprises: establishing, by the MSC server,a priority list of code type according to the call request message. 4.The method of claim 1, wherein acquiring the IP address and the portnumber assigned for the call by the wireless side BSS comprises:negotiating and establishing, by a Base Station Controller, BSC, and theMGW, an Ater interface channel between the BSC and the MGW throughcoding and rate adaption unit signaling in an in-band signaling mode ona bearer plane; acquiring the IP address and the port number assignedfor the call by the MGW and assigning its own IP address and port numberfor the call; and acquiring, by the MGW, the IP address and the portnumber assigned for the call by the BSC through the Ater interfacechannel.
 5. The method of claim 3, wherein acquiring the IP address andthe port number assigned for the call by the wireless side BSScomprises: receiving, by the MSC server, the response message containingthe IP address and the port number assigned for the call returned by theMGW; transmitting, by the MSC server, the IP address and the port numberassigned by the MGW for the call in an assignment message to a wirelessside BSS; assigning, by the wireless side BSS, an IP address and a portnumber for the call and returning the IP address and the port numberassigned for the call returned by the wireless side BSS in an assignmentresponse message to the MSC server; and transmitting, by the MSC server,information containing the IP address and the port number to the MediaGateway.
 6. The method of claim 5, wherein acquiring the IP address andthe port number assigned for the call by the wireless side BSScomprises: receiving, by the Base Station Controller, BSC, theassignment message; acquiring, by the Base Station Controller, the IPaddress and the port number of the Media Gateway; assigning, by the BaseStation Controller, the IP address and the port number for the call;initiating, by the Base Station Controller, the establishment of the IPbearer and transmitting the assignment response message containing theIP address and the port number assigned for the call by the BSC to theMSC Server; or transmitting, by the BSC, the IP address and the portnumber of the MGW to a Base Station Transceiver via signaling afterreceiving the assignment message and acquiring the IP address and theport number of the MGW; acquiring, by the Base Station Transceiver, theIP address and the port number assigned for the call by the MGW,assigning, by the Base Station Transceiver, an IP address and a portnumber of its own side for the call, reporting by the Base StationTransceiver, the IP address and the port number assigned for the call tothe BSC; then incorporating, by the BSC, the IP address and the portnumber assigned by the Base Station Transceiver in the assignmentresponse message and transmitting the assignment response message to theMSC server; and presenting, by the MSC server, the assignment responsemessage to the MGW.
 7. The method of claim 5, wherein the assignmentmessage further contains a priority list of the code type, and themethod further comprises: selecting, by the wireless side BSS, a codetype according to an order of priority in the priority list of the codetype or the BSS's own policy after receiving the assignment message, andreturning the assignment response message containing the code typeselected by the wireless side BSS to the MSC server; performing, by theMSC server, code type negotiation according to the assignment responsemessage.
 8. The method of claim 7, wherein the performing code typenegotiation according to the assignment response message comprises:receiving, by the MSC server, the assignment response message;transmitting a bearer and code type modify message to the MGW, whereinthe bearer and code type modify message carries the IP address and theport number assigned by the wireless side BSS for the call; receiving,by the MGW, the bearer and code type modify message transmitted by theMSC server, modifying code type of the wireless side end point accordingto the code type selected by the wireless side BSS, and establishing theIP bearer with the wireless side BSS.
 9. The method of claim 8, whereinthe MSC server, the wireless side BSS and the MGW are on the callingside of the call, and the performing code type negotiation according tothe assignment response message further comprises: placing, by the MSCserver on the calling side, the code type selected by the wireless sideBSS on the calling side at the first position in the priority list ofthe code type and then transmitting the priority list of the code typebackwardly to a MSC server on a called side; and distributing, by theMSC server on the called side, the acquired priority list of the codetype to the BSC on the called side; and if the wireless side BSS on thecalled side supports the code type selected by the wireless side BSS onthe calling side, the code type negotiation being successful; otherwise,feeding back, by the wireless side BSS on the called side the selectedcode type to the MSC server on the called side via the assignmentresponse message, distributing, by the MSC Server on the called side, amessage for changing the code type to a BSC on the called side or a MGWon the called side, or distributing, by the MSC Server on the calledside, a message for changing the code type to the BSC on the callingside or the MGW on the calling side via the MSC Server on the callingside; accomplishing, by the BSC on the called side or the MGW on thecalled side or the BSC on the calling side or the MGW on the callingside, conversion between the code type selected by the wireless side BSSon the calling side and the code type selected by the wireless side BSSon the called side.
 10. The method of claim 9, wherein when between theMGW on the called side and the BSC on the called side is a Time DivisionMultiplexing bearer, the method further comprises: accomplishing, by theMGW on the called side, the bearer format conversion from IP to TDM. 11.The method of claim 5, wherein after transmitting the IP address and theport number assigned by the MGW for the call in an assignment message toa wireless side BSS, the method further comprises: selecting, by thewireless side BSS, a code type; acquiring, by the MGW, a voice code typeof the BSC by adopting in-band signaling of bearer plane and comparingthe code type with the code type of core network, and, if notconsistent, inserting transcoders for conversion of voice coding; orselecting, by the wireless side BSS, a code type, returning anassignment response message containing the code type selected by thewireless side BSS to the MSC server; distributing, by the MSC server,the code type selected by the wireless side BSS to the MGW afterobtaining the code type selected; comparing, by the MGW, the code typewith the code type of the core network for consistence and, if notconsistent, inserting transcoders for transcoding.
 12. The method ofclaim 5, wherein the method further comprises: changing, by the wirelessside BSS, the code type; when determining that transcoders are disposedon the wireless side BSS, changing, by the wireless side BSS, theselected code type and reporting the selected code type to the MSCserver that initiates code type re-negotiation; or when changing orswitching the code type, initiating, by the wireless side BSS, a codetype change request; transmitting, by the MSC server, a code type changeresponse message to the wireless side BSS after finishing the change ofthe code type of corresponding end point of the MGW; and changing, bythe wireless side BSS, the code type according to the received code typechange response message.
 13. The method of claim 1, wherein the methodfurther comprises: obtaining, by the wireless side BSS, voicecompression coded payload data by removing a coding and rate adaptionunit encapsulation from the received wireless side data; andencapsulating the voice compression coded payload data in IP packets andtransmitting the IP packets to the MGW via an A interface between thewireless side BSS and the MGW.
 14. The method of claim 13, wherein afterthe MGW receives the compression coded payload data, the method furthercomprises: determining, by the MGW, a compression coding method and/oran encapsulation method used for the voice compression coded payloaddata and determining whether the compression coding method and/or theencapsulation method are the same as a compression coding method and/oran encapsulation method used on a receiving end side of the voicecompression coded payload data; if they are the same, directlytransmitting the data to the receiving end of the data; otherwiseconverting the compression coding method and/or the encapsulation methodof the data into the compression coding method and/or the encapsulationmethod on the receiving end side and transmitting the data to thereceiving end.
 15. The method of claim 14, wherein the step ofdetermining, by the MGW, the compression coding method used for thevoice compression coded payload data comprises: transmitting, by thewireless side BSS, the compression coding method used for the receivedvoice compression coded payload data to the MSC server that transmitsthe compression coding method used for the data to the MGW in turn. 16.The method of claim 15, further comprising: transmitting, by thewireless side BSS, bearer information of the data to the MSC server; andtransmitting, by the MSC server, the bearer information of the data tothe MGW; and/or receiving, by the wireless side BSS, the bearerinformation of the data transmitted by the MSC server, wherein thebearer information of the data is transmitted by the MGW to the MSC. 17.The method of claim 13, further comprising: in the Second GenerationMobile Communication System, for single rate coding, performing servicetransmission between the MGW on the calling subscriber side and the MGWon the called subscriber side, without using the user planeencapsulation method; and in the Second Generation Mobile CommunicationSystem and the Third Generation Mobile Communication System, if singlerate coding is used between the MGW on the calling subscriber side andthe MGW on the called subscriber side, performing service transmissionwithout using the user plane encapsulation method, and if multiple ratecoding is used, performing service transmission by using the user planeencapsulation method.
 18. The method of claim 17, wherein a real-timetransmission protocol encapsulation method is used for servicetransmission between the BSC and the MGW.
 19. The method of claim 1,further comprising: establishing an IP bearer between the BSC and theBase Station Transceiver for the transmitting of voice frames based onthe IP protocol.
 20. The method of claim 1, further comprising:switching a mobile station among different Base Station Transceivers ofa same BSC; and acquiring, by the BSC, an IP address and a port numberof a Base Station Transceiver of the switched party, and initiating anotification event to the MSC server to notify the MSC server ofinformation on the IP address and the port number of the Base StationTransceiver of the switched party; and changing, by the MSC server, thebearer of the Media Gateway and completing switch of the bearer.
 21. Abase station control equipment, characterized by comprising a receivingunit, a processing unit and a transmitting unit, wherein the receivingunit is configured to receive an assignment message and transmit theassignment message to the processing unit; the processing unit isconfigured to receive the assignment message, acquire an IP address anda port number of the Media Gateway contained in the message, assign anIP address and a port number for a call, initiate the establishment ofan IP bearer and transmit an assignment response message containing theIP address and the port number assigned for the call by the equipment tothe transmitting unit; and the transmitting unit is configured toreceive and transmit the assignment response message.
 22. The basestation control equipment of claim 21, wherein the receiving unit isfurther configured to receive wireless side data and the processing unitcomprises: a coding and rate adaption unit terminating module,configured to remove a coding and rate adaption unit encapsulation fromthe received wireless side data to acquire voice compression codedpayload data; and a data encapsulating module, configured to encapsulatethe voice compression coded payload data obtained by the coding and rateadaption unit terminating module in IP packets, and output the IPpackets to the transmitting unit.
 23. The base station control equipmentof claim 22, wherein the processing unit further comprises: a codeconverting module, configured to convert a code type according to a codetype modify message distributed by the Mobile Switching Center Server.24. A Media Gateway, characterized by comprising a receiving unit, aprocessing unit and a transmitting unit, wherein: the receiving unit isconfigured to receive a message for adding a wireless side end point anda bearer and code type modify message, and transmit the messages to theprocessing unit; the processing unit is configured to receive themessage for adding a wireless side end point, assign an IP address and aport number for a call, output a response message containing the IPaddress and the port number assigned for the call to the transmittingunit; receive the bearer and code type modify message, acquire, from themessage, the IP address and the port number assigned for the call by thewireless side BSS and establish an IP bearer with the wireless side BSS;and the transmitting unit is configured to receive and transmit theresponse message.
 25. The Media Gateway of claim 24, wherein: thereceiving unit is further configured to receive IP packets transmittedvia an A interface, the IP packets containing the voice compressioncoded payload data with the coding and rate adaption unit encapsulationremoved; the processing unit is further configured to convert thecompression coding method and/or the encapsulation method of the voicecompression coded payload data in the IP packets into the compressioncoding method and/or the encapsulation method used at the receiving endand then incorporating the data in the IP packets; and the transmittingunit is further configured to transmit the IP packets converted by theprocessing unit.
 26. A Mobile Switching Center Server, characterized bycomprising a receiving unit, a processing unit and a transmitting unit,wherein: the receiving unit is configured to receive a call requestmessage containing code types supported by a mobile station itself fromthe mobile station, a response message containing the IP address and theport number assigned for the call returned by the Media Gateway and anassignment response message returned by the wireless side BSS, andtransmitting them to the processing unit; the processing unit isconfigured to establish a priority list of the code type according tothe call request message, transmit a message for adding a wireless sideend point to the transmitting unit; generate an assignment messageaccording to the received response message and the priority list of thecode type and output the assignment message to the transmitting unit;conduct code type negotiation according to the received assignmentresponse message and output to the transmitting unit informationcontaining the IP address and the port number assigned for the call bythe wireless side BSS; and the transmitting unit is configured toreceive and transmit to the Media Gateway the message for adding awireless side end point and information containing the IP address andthe port number assigned for the call by the Base Station Controlleroutput by the processing unit; and receive the assignment message outputby the processing unit and transmit the assignment message to thewireless side BSS.
 27. A system for establishing a bearer for a GSMnetwork comprising a Base Station Controller, a Mobile Switching Centerserver and a Media Gateway, wherein the Media Gateway is configured toestablish an IP bearer with the Base Station Controller, wherein theMobile Switching Center server is configured to transmit a message foradding a wireless side end point to the Media Gateway, receive aresponse message returned by the Media Gateway, transmit an assignmentmessage to the Base Station Controller; receive the assignment responsemessage returned by the Base Station Controller, conduct code typenegotiation and transmit information containing the IP address and theport number assigned for the call by the Base Station Controller to theMedia Gateway; the Media Gateway is further configured to receive themessage for adding a wireless side end point transmitted by the MobileSwitching Center server, return the response message containing the IPaddress and the port number assigned for the call to the MobileSwitching Center Server; receive information on the IP address and theport number assigned for the call by the Base Station Controller andestablish an IP bearer with the Base Station Controller; and the BaseStation Controller is configured to receive the assignment messagetransmitted by the Mobile Switching Center server, acquire the IPaddress and the port number of the MGW wireless side end point containedin the message, assign the IP address and the port number for the call,initiate establishment of the IP bearer and transmit to the MobileSwitching Center server the assignment response message containing theIP address and the port number assigned for the call by the Base StationController.
 28. The system of claim 27, wherein the Base StationController is further configured to receive wireless side data, remove acoding and rate adaption unit encapsulation from the received wirelessside data to obtain voice compression coded payload data, andencapsulate the voice compression coded payload data in IP packets fortransmission; and the Media Gateway is further configured to acquire thevoice compression coded payload data encapsulated in the IP packetstransmitted by the Base Station Controller via an A interface betweenthe Base Station Controller and the Media Gateway, for subsequenttransmission.